How Much Caffeine Is Too Much? The 400 mg Limit in Real Drinks, and the Lower Limit for Sleep

How much caffeine is too much depends on what you're protecting: for general health, it's more than about 400 mg a day for most healthy adults, roughly four 8 oz cups of brewed coffee, but for sleep it can be as little as one coffee after lunch. The FDA's 400 mg figure is a daily total. Your sleep cares about how much is still in you at bedtime.

What 400 mg of caffeine looks like in real drinks

400 mg is about four 8 oz brewed coffees, two 16 oz coffees, or two and a half 16 oz energy drinks. Here's how many servings of common drinks add up to it, using typical amounts.

Real drinks vary a lot. The FDA lists a 12 oz regular brewed coffee at 113 to 247 mg, which is why it describes 400 mg as about two to three 12 oz cups. A strong coffee-shop brew gets you there faster than the table suggests. For more drinks side by side, see the caffeine in drinks chart.

How much caffeine is too much for sleep?

For sleep, too much is anything that leaves more than about 25 mg in your system at bedtime, and how much you can have shrinks through the day. The table uses the same math as our caffeine calculator: an average 5-hour half-life, so the most you can have at a given time is 25 mg doubled for every 5 hours until bed.

So with a 10:30 PM bedtime, about two coffees' worth is fine at 7 AM, one coffee is borderline at 1 PM, and by 7 PM even a cup of black tea is over. The 25 mg line isn't an official limit, just a sensible target. If you clear caffeine slowly, these numbers are too generous. How long caffeine lasts shows how much the half-life varies.

Staying under 400 mg doesn't protect your sleep

You can stay well under the daily limit and still go to bed with the equivalent of most of a coffee in you. Here's what common days leave at a 10:30 PM bedtime, adding up every drink.

That leftover caffeine matters even if you fall asleep fine. In a study that measured sleep at home with a sleep monitor, 400 mg taken 6 hours before bed cut total sleep by more than an hour.

Signs you've had too much caffeine

The FDA lists a fast heart rate, palpitations, high blood pressure, trouble sleeping, anxiety, jitters, an upset stomach, nausea and headache as signs of too much caffeine. If you get these regularly, talk to your doctor about your intake.

Very large amounts are dangerous. The FDA estimates that toxic effects such as seizures can occur with rapid intake of around 1,200 mg, less than half a teaspoon of pure caffeine powder. Avoid pure or highly concentrated caffeine products.

Who should have less than 400 mg?

Pregnant people, children and teens, and anyone with certain health conditions or medications should aim lower.

• Pregnancy: the American College of Obstetricians and Gynecologists says moderate intake, under 200 mg a day, doesn't appear to be a major factor in miscarriage or preterm birth. The FDA suggests talking to your provider if you're pregnant, trying to conceive or breastfeeding.
• Children and teens: the FDA notes that medical experts advise against energy drinks for children and teens, and that federal dietary guidelines say to avoid caffeinated drinks under age 2.
• Health conditions and medications: some make people more sensitive to caffeine. Ask your doctor or pharmacist.
• Poor sleepers: if you have trouble sleeping, cut the afternoon caffeine first, before the total.

How to cut back

Cut back gradually. The FDA says caffeine withdrawal isn't dangerous but can be unpleasant. Move your last drink 30 to 60 minutes earlier each week, or swap the afternoon one for half-caf or decaf. If tonight is already a lost cause, see what to do when you can't sleep after coffee.

Enter your own drinks and bedtime in the caffeine calculator to see your cutoff.